Geochemical and Isotopic Study of Dofan-Fantale Geothermal Prospect

Abstract

Dofan-Fantale geothermal prospect is one of the geothermal fields in Ethiopia that was recommended for further study by UNDP (1973). Currently detailed geological, geochemical and geophysical studies are going on. Dofan-Fantale area is located in the Southern Afar Region, at Ethiopian Rift Valley, which is about 200km NE of the capital, Addis Ababa. Twenty-eight water samples from thermal springs, boreholes, lakes, rivers, and dug wells were collected in the area under study. Water chemistry suggests the existence of NaHCO3, CaHCO3 and Na/ClHCO3 water types. The reservoir temperature as indicated from the geothermometry results of Habilo spring (Sp-4) is close to ~250?C. Water - mineral equilibria study has shown that most of the common geothermal minerals are over saturated at ~100C? at atmospheric pressure. However, they are found to be in equilibrium with the rock reservoir at a temperature of ~250?C at depth. The ?2H versus ?18O plot has revealed ®18O - shift® of 1.4 â for Habilo thermal feature (Sp-4), which might indicate higher circulation period and longer residence time.